Patent Literature (PTL) 1 discloses a detection device which detects whether a human hand is in contact with a steering wheel, taking advantage of characteristics of an oscillator circuit in that the frequency of the oscillator circuit changes as capacitance changes.
Meanwhile, PTL 2 discloses a vehicle seat apparatus which makes use of a seat heater to detect whether a passenger is being seated. The vehicle seat apparatus serves as a seat heater and also as an electrode for detecting whether the passenger is being seated. Thus, an oscillator circuit is obviated, and cost is reduced.
FIG. 17 is a block diagram of the vehicle seat apparatus disclosed in PTL 2.
Seat heater 8 is provided in a seat of vehicle seat apparatus 1, and connected via coupling capacitor 22 to seating detection circuit 14. Seat heater 8 is supplied with power via seat-heater release switches 11 and 12. Seating detection circuit 14 detects passenger's action of seating himself/herself on vehicle seat apparatus 1, when seat-heater release switches 11 and 12 are off.
FIG. 18 is a diagram showing an equivalent circuit at a time when the vehicle seat apparatus shown in FIG. 17 detects whether the passenger is being seated.
Seating detection circuit 14 is connected via coupling capacitor 22 to seat heater 8, parasitic capacitance C11 and C12, and capacitance C13, as shown in the figure. Herein, parasitic capacitance C11 and C12 represent parasitic capacitance generated by seat-heater release switches 11 and 12, respectively, when seat-heater release switch 11 and seat-heater release switch 12 are off. Capacitance C13 has one electrode corresponding to seat heater 8 and the other electrode corresponding to a human body.
Capacitance C13 when a person is being seated on vehicle seat apparatus 1 is greater than when the person is not seated on vehicle seat apparatus 1. Seating detection circuit 14 detects whether the person is being seated, based on the magnitude of capacitance C13.
Typically, seat-heater release switches 11 and 12 are placed into a conductive state (on) to warm the heater, and placed into a blocked state (off) to operate seating detection circuit 14.